what is the concept behind Tense Consistency??

Tenses are tools used to indicate when a situation or action takes place i.e. to show the position of the situation with respect to time.

The tenses in the main clause and the subordinate clause of a sentence need to be consistent with their relationship that is implied by the sentence.

Suppose, the tense in the main clause is simple present tense.

E.g. She feels that the current system is biased against women.

Suppose the subordinate clause is as follows:

As Sheila failed to land a job in any of the big consulting companies, she feels that the current system is biased against women.

The tense of the verb in the subordinate clause is not consistent with the relationship that is implied by the sentence. As the sentence implies that Sheila is unable to find a job from some point in the past to now, the correct tense for the subordinate clause will be present perfect tense.

Hence the correct statement is as follows:

As Sheila has failed to land a job in any of the big consulting companies, she feels that the current system is biased against women.